This invention relates generally to actuators for positioning control of devices coupled thereto and more particularly to electrically controlled actuators for positioning of valves, mechanical dampers and the like as employed in process control systems. The invention is particularly suited for use in systems related to heating, ventilating and air conditioning applications.
Process control systems frequently employ valves which may be positionably adjusted for controlling the flow of fluids within a conductor system such as a pipeline. Other types of fluid flow controlling devices often encountered in process control systems include dampers which may be actuated for controllably modulating the flow of gases therethrough. One type of process control system in which the rotary actuator of the present invention may be advantageously used includes heating, ventilating and air conditioning (HVAC) systems which usually employ a plurality of air handling units comprising interconnected ductwork having mechanical dampers associated therewith. The ductwork and dampers cooperate for controlling the flow of outside ambient air into a conditioned space, for controlling the flow of air from the space to the ambient and for controlling air flow between cool and warm air ducts. HVAC systems also employ actuator-positioned valves whereby the flow of chilled or heated water through heat exchanger coils may be controlled in accordance with the air temperature which is desired to be maintained as the air passes over such coils for air temperature-regulating purposes. Liquid flow control valves and fluid controlling dampers of the aforementioned type are available in a wide variety of sizes and torque requirements, such sizes being generally related to the size of the air handling unit with which they may be associated. While it is known to utilize electrically-driven rotary actuators for positioning such valves and dampers, the wide range of torque requirements of such devices has heretofore necessitated that such actuators be configured in a variety of drive motor torque output ranges, enclosure sizes and gearing arrangements. Further, the relatively recent advent of sophisticated control equipment including computerized direct digital control systems utilizing algorithms for effecting sophisticated control strategies has required that such rotary actuators have the capability of being readily adapted to respond to and be controlled by low voltage digital signals. The result of these widely disparate application requirements has been a proliferation of electrically-controlled rotary actuators which impose unnecessary complexities upon the manufacturing, warehousing and field installation functions.
An electrically-controlled rotary actuator which takes maximum advantage of parts commonality and is adapted to be configured for providing any one of several rated output torques, which includes a power transmission having drive elements capable of being formed of several disparate materials selected in view of such torque requirements and which is adapted to respond to and be controlled by low voltage digital signals would be a significant advance over the prior art.